North Vietnam, 10.Anniversary of the Geneva Agreement, July 20th, 1964, Michel Nr. 325-326; Two stamps with the nominals of 12 xu were issued in perforation 11.0.
Mint set in blocks of four:
Very rare local letter franked with a single 12xu stamp of the set and cancelled with a Hanoi machine cancel in September of 1964. The letter was mailed from Hanoi to Ha Dong. Most local letters were destroyed in the multi-decadal war, the tropical climate or recycling due to raw material shortages.
Letter mailed one day after the first day issuance to Klewitz in West Germany. The letter features the entire set plus some additional North Vietnamese stamps for an overall postage of 52 xu. That was slightly in excess of the standard letter rate to West Germany of 50 xu.
Mixed franking using two of the 12xu Costumes stamps plus other NVN stamps for an overall franking of 60xu (Probably over-franked) on an air-mail letter to East Germany.
Mixed franking with the entire set plus other NVN stamps (including the 12 xu Geneva Agreement stamp) for an overall postage of 97xu, which was well above the required 12xu tariff in 1964, so most likely this represents a philatelic mailing.